speedyz

POR-15 works very well! Stuff is as tuff as steel once it hardens.

I am having the same problem with my '75 280. I have replaced the halfshaft U-joints ($200.00). That didn't help. The problem seemed to get worse after I flushed the diff with fresh heavy weight oil. I just ordered a new diff mount. I will try that as well as replacing the diff with one I got off of some race buddies from a later model Z. My fear is that the problem lies in the driveshaft. Those U-joints can't be replaced. A new one with replaceable U-joints is $230.00. My family car, '92 Ford Crown Vic, had a similar problem with the loud whirrrr coming from the rear end and it was just frozen up drive shaft U-joints. The Z, however, has so much more back there that can go bad. I will let you know how all these changes work once I get them completed in the next few weeks.